Long-term ultraviolet A irradiation of the eye induces photoaging of the skin in mice.

Abstract

Irradiation by long-term ultraviolet (UV) A initiates the induction of photoaging.
However, the mechanisms responsible for the structural changes of skin induced by
UVA irradiation of the eye are still unknown. Male hairless mice were used in this
study. The eye or dorsal skin was locally exposed to UVA after covering the remaining
body surface with aluminum foil at a dose of 110 kJ/m(2) using a FL20SBLB-A lamp for
60 days. The plasma α-melanocyte stimulating hormone (α-MSH), nitrogen oxides (NO(2)/NO(3)),
tumor necrosis factor-α (TNF-α), and the prostaglandin E(2) (PGE(2)) content all increased
after UVA irradiation. The levels of NO(2)/NO(3), TNF-α, and PGE(2) also increased
more after UVA skin irradiation than after UVA eye irradiation. However, the level
of α-MSH increased more by eye irradiation than skin irradiation. In addition, UVA
irradiation of the eye and dorsal skin increased the number of mast cells and fibroblasts.
Furthermore, the expression of the melanocortin-1 receptor (MC1R) was increased on
the fibroblast surface by UVA irradiation of the eye. These results indicate that
the signal evoked by UVA irradiation of the eye, through the hypothalamo-pituitary
proopiomelanocortin system, up-regulated the production of α-MSH. This hormone controls
the collagen generation from fibroblasts, thus suggesting that photoaging was induced
by UVA irradiation of the eye.